Two-section type pickproof lock assembly

Abstract

A pickproof lock assembly has two lock sections which can be opened by a single key. The first lock section includes a key plug and a first set of tumbler members which engage radial pits provided on the key so as to disengage the key plug from the lock shell. The second lock section includes first and second movable plug halves disposed inside the lock shell and a second set of tumbler members. The key has axially extending curve protrusions on one end to move the first and second plug halves and align groove-free spaces on the surface of the first and second plug halves to form a continuous annular path. The second set of tumbler members contacts the first and second plug halves at the annular path to permit rotation of the key plug relative to the lock shell. When non-alignment of the groove-free space of the first and second plug halves occurs due to insertion of a wrong key, rotation of the key plug by the wrong key causes the second set of tumbler members to engage notches on the surface of the first and second plug halves and prevent further rotation of the key plug.

I claim: 
     
       1. A lock assembly, comprising: a lock shell having a front end, a rear end a longitudinal opening accessible from said front end, and an inner surface provided with a set of first tumbler holes disposed adjacent to said front end and a set of second tumbler holes disposed adjacent to said rear end;   a driving shaft axially disposed in said longitudinal opening and having a transverse head portion, a tail portion journaled on said rear end of the lock shell, and a shaft portion which is rectangular in cross-section;   first and second plug halves received in said longitudinal opening and cooperatively forming a cylindrical member in sliding contact with said inner surface of said lock shell, each of said first and second plug halves having a clamping face provided with an axial first notch, said first notch of said first and second plug halves cooperatively confining a rectangular receiving space, said shaft portion of said driving shaft extending into said rectangular receiving space and being clamped by said first and second plug halves, each of said first and second plug halves having a curved surface formed with at least one axially extending second notch which opens from a first end of said first and second plug halves and having a terminating end spaced: from a second opposite end of said first and second plug halves to provide a groove-free space between said second end of said first and second plug halves and said terminating end of said second notch;   a biasing means to bias each of said first and second plug halves toward said transverse head portion of said driving shaft;   a key plug rotatably mounted to said lock shell inside said longitudinal opening adjacent to said front end, said key plug being formed as an annular wall confining an axial key way and having a set of third tumbler holes aligned with said first tumbler holes when said lock assembly is in a locked position, and a   rear end provided with first and second axially extending arc projections to engage said transverse head portion of said driving shaft;   a first set of holding means resiliently extending through said first and third tumbler holes into said key way to engage said lock shell and said key plug when said lock assembly is in said locked position;   a second set of holding means resiliently extending through said second tumbler holes into said longitudinal opening; and   a key having a cylindrical key body provided with radial pits, and a front end formed with first and second axially extending curve protrusions which define a receiving groove therebetween, said first and second curve protrusions having different lengths;   said key being inserted in said key way such that said first set of tumbler means engage said radial pits so as to engage said key body with said key plug and disengage said lock shell from said key plug thus permitting rotation of said key plug relative to said lock shell, said curve protrusions moving said first and second plug halves away from said transverse head portion against said biasing means to align said groove-free space of said first and second plug halves and form a continuous annular path, said second set of tumbler means contacting said first and second plug halves at said annular path to permit rotation of said key relative to said lock shell;   whereby, when non-alignment of said groove-free space of said first and second plug halves occurs due to insertion of a wrong key into said key way, rotation of said key plug by the wrong key causing said second set of tumbler means to engage said second notch of said first and second plug halves and prevent further rotation of the wrong key and said key plug relative to said lock shell.   
     
     
       2. The lock assembly as claimed in claim 1, further comprising: said lock shell having a wall portion extending inwardly into said longitudinal opening of said lock shell and being spaced from said rear end of said lock shell, and a pair of spaced axially extending leg receiving bores provided on said rear end;   a staple member having a shorter leg and a longer leg received in a longer one of said leg receiving bores, and a staple spring received in said longer one of said leg receiving bores, said staple spring being attached to said longer leg of said staple member and biasing said staple member outwardly from said leg receiving bores; and   an oblong control plate disposed between said wall portion and said rear end of said lock shell and extending between said leg receiving bores, said tail portion of said driving shaft extending through said wall portion to engage and rotatably drive said control plate, said driving shaft being rotated with said key to correspondingly rotate said control plate between a first position, wherein said control plate engages and retains said shorter leg of said staple member at a shorter one of said leg receiving bores to place said staple member in a locked position, and a second position, wherein said control plate disengages said shorter leg of said staple member to cause expansion of said staple spring and release of said shorter leg from said shorter one of said leg receiving bores to place said staple member in an unlocked position.